from kivy.app import App

from kivy.uix.gridlayout import GridLayout
from kivy.uix.widget import Widget
from kivy.uix.button import Button
from kivy.uix.label import Label
from kivy.uix.boxlayout import BoxLayout

from kivy.config import Config

Config.set('graphics', 'resizable', 0)
Config.set('graphics', 'width', 400)
Config.set('graphics', 'height', 500)


class CalculatorApp(App):

    def update_label(self):
        self.lbl.text = self.formula

    def add_number(self, instance):
        if(self.formula == '0'):
            self.formula = ''

        self.formula += str(instance.text)
        self.update_label()

    def add_operation(self, instance):
        if(str(instance.text).lower() == 'x'):
            self.formula += '*'
        else:
            self.formula += str(instance.text)

        self.update_label()

    def calc_operation(self, instance):
        self.lbl.text = str(eval(self.lbl.text))
        self.formula = '0'


    def build(self):
        self.formula = '0'
        b1 = BoxLayout(orientation='vertical', padding=25)
        g1 = GridLayout(cols=4, spacing=2, size_hint=(1, .6))

        self.lbl = Label(text='0',
            font_size=40,
            size_hint=(1, .4),
            halign="right",
            text_size=(400 - 50, 500 * .4 - 50)
            )

        b1.add_widget(self.lbl)

        g1.add_widget( Button(text='7', on_press=self.add_number) )
        g1.add_widget( Button(text='8', on_press=self.add_number) )
        g1.add_widget( Button(text='9', on_press=self.add_number) )
        g1.add_widget( Button(text='X', on_press=self.add_operation))

        g1.add_widget( Button(text='4', on_press=self.add_number) )
        g1.add_widget( Button(text='5', on_press=self.add_number) )
        g1.add_widget( Button(text='6', on_press=self.add_number) )
        g1.add_widget( Button(text='-', on_press=self.add_operation))

        g1.add_widget( Button(text='1', on_press=self.add_number) )
        g1.add_widget( Button(text='2', on_press=self.add_number) )
        g1.add_widget( Button(text='3', on_press=self.add_number) )
        g1.add_widget( Button(text='+', on_press=self.add_operation))

        g1.add_widget( Button(text='/', on_press=self.add_operation))
        g1.add_widget( Button(text='0', on_press=self.add_number))
        g1.add_widget( Button(text='.', on_press=self.add_number))
        g1.add_widget( Button(text='=', on_press=self.calc_operation))

        b1.add_widget(g1)

        return b1



if __name__ == "__main__":
    CalculatorApp().run()